In short; a System State backup that includes all volumes of the ADFS server will be sufficient for ADFS disaster recovery (assuming AD is still present).
A more extended Technet article is also available on http://technet.microsoft.com/en-us/library/cc787348(v=WS.10).aspx.
If SQL is being used rather than WID then a backup of the ADFS configuration database on the target SQL server being used is also required for ADFS recovery.